Display device

ABSTRACT

In a display device, a backlight unit emits light forward. Picture elements are arranged in columns and rows to define a picture element plane and each of the picture elements has a transmitting region to transmit light coming from the backlight unit. Collecting elements are arranged in front of the backlight unit to transmit and collect the light on the picture element plane. Each collecting element is associated with the transmitting region of one of the picture elements. The light transmitted through each collecting element forms a beam spot on the picture element plane. The center of the beam spot is located within the transmitting region associated with the collecting element. Two beam spots, formed on two picture elements that are adjacent to each other in a row direction, have their centers of mass shifted from each other in a column direction on the picture element plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a display device and moreparticularly relates to a non-emissive display device that conducts adisplay operation using the light emitted from a backlight unit.

2. Description of the Related Art

Examples of non-emissive display devices include liquid crystal displays(LCDs), electrochromic displays, and electrophoretic displays. Amongother things, LCDs are currently used extensively in personal computers,cell phones and many other electronic devices.

An LCD is designed to display images, characters and so on by changingthe optical properties of its liquid crystal layer at the openings ofits picture element electrodes, which are regularly arranged in a matrixpattern, with drive voltages applied to those electrodes. Also, in theLCD, each picture element includes a thin-film transistor (TFT) as aswitching element in order to control the respective picture elementsindependently of each other.

However, if each picture element includes a transistor, then the area ofeach picture element decreases and the brightness drops.

Furthermore, considering their electrical performance, manufacturingtechniques and other constraints, it is difficult to reduce the sizes ofswitching elements and interconnects to less than certain limits. Forexample, an etching precision achieved by a photolithographic process isusually about 1 μm to about 10 μm. Accordingly, as the definition of anLCD has been further increased and as the size thereof has been furtherdecreased, the picture element pitch becomes smaller and smaller. As aresult, the aperture ratio further decreases and the brightness furtherdrops.

To overcome this low-brightness problem, according to a proposed method,a collecting element may be provided for each of the huge number ofpicture elements of an LCD so that the light emitted from a backlightunit is collected on each of those picture elements.

For example, Japanese Laid-Open Publication No. 2-12224 discloses atransmissive color LCD that uses microlenses. In the LCD of that type, anumber of microlenses are arranged as densely as possible on atwo-dimensional plane, thereby realizing a bright display as shown inFIG. 15B. Since the microlenses are arranged in such a densest possiblepattern, R, G and B color filters (and their associated pictureelements) are arranged in a delta pattern such that every set of RGBcolor filters on a row is shifted from its associated set of RGB colorfilters on the previous row by one and a half pitches as shown in FIG.15A. That is to say, the ratio of the picture element pitch in the xdirection (i.e., row direction) to the picture element pitch in the ydirection (i.e., column direction) is 2:√{square root over ( )}3.

However, to realize the microlens arrangement disclosed in JapaneseLaid-Open Publication No. 2-12224, the picture elements of an LCD needto be arranged in the delta pattern at the predetermined pitch.

An LCD with such a delta picture element arrangement achieves thedisplay of a natural video, and therefore, can be used effectively in TVsets, camera finders and so on. However, to present characters, figuresand other objects including a lot of lines on personal computers, cellphones and so on, the LCD preferably adopts not so much the deltaarrangement as a striped arrangement. In the striped arrangement,normally three rectangular R, G and B picture elements make up onesubstantially square pixel as shown in FIG. 16. The microlensarrangement of Japanese Laid-Open Publication No. 2-12224 cannot beapplied to any LCD with this striped arrangement.

There is an increasing demand for further improvement of opticalefficiency in various other non-emissive display devices as well, notjust the LCDs described above.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, an object of thepresent invention is to provide a display device that can improve theoptical efficiency without being limited by the arrangement of pictureelements by modifying the arrangement of collecting elements (i.e.,light-collecting elements or optical condensing elements) associatedwith the picture elements.

A display device according to a preferred embodiment of the presentinvention preferably includes a backlight unit, a plurality of pictureelements, and a plurality of collecting elements. The backlight unitpreferably emits light forward. The picture elements are preferablyarranged in columns and rows to define a picture element plane and eachof the picture elements preferably has a transmitting region to transmitthe light that has come from the backlight unit. The collecting elementsare preferably arranged in front of the backlight unit to transmit andcollect the light on the picture element plane. Each and every one ofthe collecting elements is preferably associated with the transmittingregion of one of the picture elements. The light that has beentransmitted through each said collecting element preferably forms a beamspot on the picture element plane. The center of the beam spot ispreferably located within the transmitting region associated with thecollecting element. Two beam spots, which are formed on two of thepicture elements that are adjacent to each other in a row direction,preferably have their centers of mass shifted from each other in acolumn direction on the picture element plane.

In one preferred embodiment of the present invention, the pictureelements are preferably arranged at a pitch P1 in the row direction andinclude first, second and third picture elements that are adjacent toeach other in the row direction. In the first, second and third pictureelements, the size of the collecting element associated with thetransmitting region of at least the first picture element is preferablygreater than P1 as measured in the row direction.

In this particular preferred embodiment, the size of the collectingelement associated with the transmitting region of the second pictureelement and the size of the collecting element associated with thetransmitting region of the third picture element are preferably bothgreater than P1 as measured in the row direction.

In another preferred embodiment, the picture elements are preferablyarranged at a pitch P1 in the row direction and preferably includefirst, second and third picture elements that are adjacent to each otherin the row direction. As measured in the row direction, the size of thecollecting element associated with the transmitting region of the firstpicture element is preferably different from that of the collectingelement associated with the transmitting region of the second pictureelement.

In still another preferred embodiment, the display device may furtherinclude a color filter layer including red, green and blue colorfilters, which are arranged in a striped pattern.

In yet another preferred embodiment, the collecting elements may make upan array of microlenses.

In yet another preferred embodiment, each said picture element may havea liquid crystal layer.

In that case, each said picture element preferably has a reflectingregion to reflect the light that has come from the front of the displaydevice can selectively conduct a display operation either in atransmission mode or in a reflection mode.

More specifically, the transmitting region of each said picture elementis preferably arranged such that the center of the transmitting regionsubstantially matches that of the beam spot.

A display device according to a preferred embodiment of the presentinvention modifies the arrangement of collecting elements, which areassociated with respective picture elements, thereby improving theoptical efficiency without being limited by the arrangement of pictureelements, for example. Also, in a preferred embodiment, the brightnessof a particular color is increased, thereby changing the brightness on acolor-by-color basis and realizing an even more viewable display. Also,when the present invention is implemented as a transflective LCD, thebrightness ratio between the reflection and transmission modes can bechanged without changing the area ratio between reflective andtransmissive electrodes.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically illustrating a transflectiveLCD according to a specific preferred embodiment of the presentinvention.

FIG. 2 is a plan view schematically illustrating an exemplary positionalrelationship among a microlens, the center of a beam spot and itsassociated transmitting region in the LCD shown in FIG. 1.

FIG. 3 is a plan view schematically illustrating another exemplarypositional relationship among a microlens, the center of a beam spot andits associated transmitting region in the LCD shown in FIG. 1.

FIG. 4 is a plan view schematically illustrating the arrangement ofmicrolenses and centers of beam spots in a comparative example.

FIG. 5 is a plan view schematically illustrating the arrangement ofmicrolenses and centers of beam spots in another comparative example.

FIG. 6 is a plan view schematically illustrating an exemplary positionalrelationship among a microlens, the center of a beam spot and itsassociated transmitting region when the picture elements are arranged ina delta pattern.

FIG. 7 is a plan view schematically illustrating an exemplary positionalrelationship among microlenses, beam spot centers and their associatedtransmitting regions in a situation where only the microlensesassociated with the transmitting regions of R, G or B picture elementshave an increased diameter.

FIG. 8 is a cross-sectional view schematically illustrating a backlightunit for use in the transflective LCD shown in FIG. 1.

FIG. 9 is a graph showing the optical properties of the backlight unitas measured on the light outgoing plane thereof.

FIG. 10 is a schematic representation showing how to measure the opticalproperties on the light outgoing plane of the backlight unit.

FIG. 11A schematically illustrates the dispersion of the directivityshown in FIG. 9.

FIG. 11B shows what the ellipses shown in FIG. 11A mean.

FIG. 12 illustrates the light guide plate of the backlight unit shown inFIG. 8.

FIG. 13 is a plan view illustrating the TFT substrate of a transflectiveliquid crystal panel for use in the transflective LCD shown in FIG. 1.

FIG. 14 is a partial cross-sectional view of the liquid crystal panelincluding the TFT substrate shown in FIG. 13 as viewed on the planesindicated by XIV-XIV in FIG. 13.

FIG. 15A is a schematic representation showing the delta arrangement ofpicture elements as disclosed in Japanese Laid-Open Publication No.2-12224.

FIG. 15B is a schematic representation showing the lens arrangementthereof.

FIG. 16 is a schematic representation showing a striped picture elementarrangement.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

The following illustrative embodiments of the present inventions aresupposed to be applied to a semi-transmissive (or transflective) LCD.However, the present invention is in no way limited to those specificpreferred embodiments but may be naturally applicable for use innon-transflective LCDs such as a transmissive LCD. Furthermore, thepresent invention can also be used effectively in electrophoreticdisplays and other non-LCD displays.

A transflective LCD has recently been developed as an LCD that can beused effectively even in a bright environment and may be applicable foruse in a cell phone, for example. In the transflective LCD, each pictureelement includes a transmitting region to transmit the light coming froma backlight and a reflecting region to reflect the ambient light. Thus,the transflective LCD can switch its modes of display according to theoperating environment from transmission mode into reflection mode, orvice versa, and may even use both of these modes at the same time. Atransflective LCD is disclosed more fully in Japanese Laid-OpenPublication No. 11-109417, for example.

A conventional transflective LCD needs a relatively broad reflectingregion. Accordingly, the ratio of the area of the transmitting region tothat of each picture element may decrease so much that the brightnessmay drop in the transmission mode. However, the transflective LCD of thefollowing preferred embodiment of the present invention can increase thebrightness in the transmission mode with the decrease in brightness inthe reflection mode minimized.

FIG. 1 schematically illustrates a transflective LCD 200 according to aspecific preferred embodiment of the present invention.

The transflective LCD 200 includes a backlight unit 50 (not shown inFIG. 1 but in FIG. 8), a group 54 of collecting elements provided infront of the backlight unit 50, and a display panel 100 provided infront of the group of collecting elements 100. It should be noted thatwhen some member is located “in front of” another member, the formermember is supposed herein to receive the light from the backlight unitlater than the latter member does.

The display panel 100 includes a pair of transparent substrates 10 and11 and a plurality of picture elements Px that are arranged in columnsand rows between those substrates 10 and 11. The picture elements Pxinclude R, G and B picture elements that emit red, green and blue lightrays, respectively. Each of those picture elements Px is defined by alight shielding layer (i.e., black matrix) BL1 extending in the rowdirection and another light shielding layer BL2 extending in the columndirection. The light shielding layer BL1 may be defined by gate lines 1(see FIG. 13) while the light shielding layer BL2 may be defined by datalines 2 (see FIG. 13, too).

The display panel 100 further includes a color filter layer (not shown)including red (R) color filters, green (G) color filters and blue (B)color filters. These R, G and B color filters are arranged in stripes asshown in FIG. 16. Three picture elements Px, which are adjacent to eachother in the row direction, transmit R, G and B light rays through theR, G and B color filters, respectively, and together make up one pixel.Each of those picture elements Px includes a transmitting region Tr anda reflecting region Rf. The transmitting region Tr is a region toconduct a display operation in transmission mode, while the reflectingregion Rf is a region to conduct a display operation in reflection mode.

In the transflective LCD 200, the group 54 of collecting elementsincludes a plurality of collecting elements 54 a, each of which isassociated with the transmitting region Tr of one of the pictureelements Px. In this preferred embodiment, an array of microlenses isprovided as the group 54 of collecting elements 54 a.

In the microlens array 54, each of the microlenses 54 a is provided forthe transmitting region Tr of its associated picture element Px. A lightray 41, passing through a microlens 54 a, form a beam spot on a planethat is defined by the picture elements (which will be sometimesreferred to herein as a “picture element plane”) and the center of thatbeam spot is located within the transmitting region Tr of its associatedpicture element Px.

In this preferred embodiment, each color light ray is collected withinthe transmitting region Tr of its associated picture element Px.However, not every color ray has to be collected within the transmittingregion Tr but a color ray that has passed through a microlens 54 a maybe collected at a point that is closer to the microlens 54 a than to thepicture element plane. Alternatively, another color ray that has passedthrough another microlens 54 a may be collected at a point that is moredistant from the microlens 54 a than the picture element is. Still, eachcolor ray is preferably collected within the transmitting region Tr ofits associated picture element, because the brightness can be kept highenough even when the area of the transmitting region Tr is reduced.

It should be noted that the “beam spot” refers to herein the beam crosssection (or profile) of a color ray on the picture element plane unlessstated otherwise. Thus, the “beam spot” does not necessarily mean a“focal point” (i.e., a point at which the color ray has the smallestcross section). Also, the “center of the beam spot” is defined herein inview of the light intensity distribution on the picture element planeand corresponds to the center of mass of a piece of paper, of which theshape is defined by the beam cross section of the beam spot and whichhas a density distribution corresponding to the light intensitydistribution. If the light intensity distribution is symmetric withrespect to the geometric center of the beam cross section of the beamspot, then the “center of the beam spot” matches the geometric center.However, if the light intensity distribution is asymmetric due to theaberration of the microlens, for example, then the “center of the beamspot” deviates from the geometric center.

The transflective LCD 200 of this preferred embodiment is characterizedby arranging the collecting elements in a predetermined pattern suchthat two beam spots, which are formed on two of the picture elementsthat are adjacent to each other in the row direction, have their centersof mass shifted from each other in the column direction on the pictureelement plane.

In this case, the “center of mass” of a beam spot matches the “center”of the beam spot if a single beam spot center is formed on a singlepicture element. However, if multiple beam spot centers are formed on asingle picture element, then the “center of mass” of the beam spot isdefined with respect to those beam spot centers.

Hereinafter, the specific arrangement of the microlens array in the LCDof this preferred embodiment will be described more fully with referenceto FIGS. 2 through 7, which are plan views of the microlens array asviewed perpendicularly to the display screen. In FIGS. 2 through 7, thecenter of each microlens is supposed to match that of its associatedbeam spot for the sake of simplicity.

FIG. 2 is a plan view schematically illustrating an exemplary positionalrelationship among a microlens 54 a, the center 41C of a beam spot andits associated transmitting region Tr in the LCD 200. The pictureelements are arranged in stripes at a pitch P1 in the row direction andat a pitch P2 in the column direction. Three picture elements Px thatare adjacent to each other in the row direction transmit R, G and Blight rays, respectively, and together make up one pixel. Themicrolenses 54 a are arranged such that the center 41C of each beam spotis formed within its associated transmitting region Tr and substantiallymatches the center of that transmitting region Tr. In the exampleillustrated in FIG. 2, the microlenses are arranged as densely aspossible with respect to the picture elements that are arranged instripes.

A single beam spot center 41C is formed in each picture element Px.Thus, the center 41C of each beam spot matches the center of massthereof. As shown in FIG. 2, the respective centers 41C of multiple beamspots are arranged in a zigzag pattern along a row of picture elements.The centers 41C of beam spots on two arbitrary picture elements Px,which are adjacent to each other in the row direction, are shifted fromeach other in the column direction. In other words, there is no pair ofbeam spots, of which the centers 41C are aligned with each other in thecolumn direction. By arranging the microlenses such that the center ofthe microlenses (i.e., the centers of beam spots), associated with twoadjacent picture elements on a row, are shifted from each other in thecolumn direction in this manner, the microlenses can also be arranged asdensely as possible even with respect to picture elements that arearranged in stripes. In the arrangement disclosed in Japanese Laid-OpenPublication No. 2-12224 mentioned above, the centers of microlenses(i.e., the centers of beam spots), associated with each row of pictureelements, are aligned with each other in the column direction. Thus, toarrange the microlenses as densely as possible, the picture elementsneed to be arranged in a delta pattern as described above.

As shown in FIG. 2, the beam spot centers 41C are arranged in a zigzagpattern such that two rows of beam spot centers 41C are formed on eachrow of picture elements so as to be located at two mutually differentlevels in the column direction. On each of the two rows of beam spotcenters 41C, the beam spot centers 41C are arranged at a pitch Mx of 2P1in the row direction. That is to say, on the same row of pictureelements, the two rows of beam spot centers 41C have their pitchesshifted by Mx/2 (=P1). Also, in this preferred embodiment, the pictureelements Px and beam spot centers 41C are arranged such that theirpitches P2 and My in the column direction satisfy P2=2My. Accordingly,the microlenses 54 a with a circular cross section can be arranged in anideal pattern (i.e., as densely as possible) on a plane that is parallelto the display screen. The microlenses 54 a shown in FIG. 2 satisfyMx:My=2: √{square root over ( )}3 and the fill density of themicrolenses 54 a on a microlens array plane (i.e., a plane that isdefined parallel to the display screen) is maximized at π√{square rootover ( )}3/6=0.906. Accordingly, 90.6% of the overall quantity of lightthat has been incident from the backlight unit 50 on the display panel100 can be collected onto associated transmitting regions and can beused for display purposes. For that reason, even if the area of eachtransmitting region were reduced as the definition of a liquid crystalpanel is further increased, a bright transmission mode could still beachieved. Also, even if the area ratio of each transmitting region toits associated picture element Px were reduced to increase thebrightness in a reflection mode, a bright transmission mode could stillbe achieved, too. Furthermore, the brightness ratio between thereflection and transmission modes can be changed without changing thearea ratio between the reflective and transmissive electrodes bymodifying the lens design.

FIGS. 4 and 5 are plan views schematically illustrating exemplaryarrangements of microlenses and beam spot centers in comparativeexamples.

In the microlens arrangement shown in FIG. 4, if the ratio of thepicture element pitch P1 in the row direction to the picture elementpitch P2 in the column direction is 1:3 as in a normal arrangement, themicrolenses 254 a have a fill density of at most π/12=0.262.Accordingly, the maximum quantity of light that can be used in thetransmission mode display operation is 26.2% of the overall quantity oflight that has been incident on the liquid crystal panel from thebacklight unit.

In the arrangement shown in FIG. 5 in which three microlenses 255 a arearranged for each picture element Px, if P1:P2=1:3, the microlenses 255a have a fill density of at most π/4=0.785. Accordingly, the maximumquantity of light that can be used in the transmission mode displayoperation is 78.5% of the overall quantity of light that has beenincident on the liquid crystal panel from the backlight unit.

In the example illustrated in FIG. 2, each microlens has a circularcross section on a plane that is defined parallel to the display screen.However, the lenses to be used in the LCD 200 do not have to have such acircular cross section. Alternatively, the lenses may have a hexagonalcross section as shown in FIG. 3, for example. In the microlens arrayshown in FIG. 3, multiple rectangular hexagonal microlenses 55 a arearranged in a honeycomb pattern. This microlens array is designed suchthat every side of each microlens 55 a contacts with a side of anadjacent microlens 55 a. Accordingly, on the microlens array plane, themicrolenses 55 a can be arranged at a fill density of almost 100%.Consequently, compared to the microlenses 54 a shown in FIG. 2, the lensfill density can be further increased and a brighter transmission modeis realized.

Thus, it can be seen that the incoming light for the LCD can be usedmore effectively in the microlens arrangements shown in FIGS. 2 and 3than in the comparative examples shown in FIGS. 4 and 5.

In the preferred embodiment described above, the picture elements Px arearranged in stripes in the LCD 200. Alternatively, the picture elementsPx may also be arranged in a delta pattern, for example.

FIG. 6 is a plan view schematically illustrating an exemplary positionalrelationship among a microlens 56 a, the center of a beam spot 41C andits associated transmitting region Tr when the picture elements Px arearranged in a delta pattern. Even though the picture elements Px arearranged in such a delta pattern, the beam spot centers 41C shown inFIG. 6 are arranged just like the beam spot centers 41C shown in FIG. 2.

In the preferred embodiments of the present invention described above,the microlenses are arranged either as densely as possible or at leastrather densely. However, the present invention is in no way limited tothose specific preferred embodiments.

Rather, by getting the centers of microlenses (i.e., the centers of beamspots), associated with two picture elements that are adjacent to eachother on a picture element row, shifted from each other in the columndirection, the microlenses can be arranged in various other patterns andnumerous effects are achievable.

First, as already described for the densest possible arrangement, thediameter of the microlens 54 a may be greater than the picture elementpitch P1 in the row direction. Accordingly, the optical efficiency canbe increased by using bigger microlenses than those shown in FIGS. 4 and5 without being limited by the picture element pitch P1.

In the examples illustrated in FIGS. 2, 3 and 6, the size of each of themultiple microlenses as measured in the row direction is greater thanthe picture element pitch P1. However, the present invention is in noway limited to those specific preferred embodiments. If the size of eachmicrolens as measured in the row direction is greater than the pictureelement pitch P1, then the light coming from the backlight unit can becollected on the transmitting region more effectively compared to thesituation where that size is less than the pitch P1. Nevertheless, thesize of the microlens may be appropriately determined according to thearea ratio of the transmitting region to the picture element Px and thelocation of the transmitting region in the picture element Px. Thus, thesize of the microlens in the row direction may be less than the pictureelement pitch P1. Even so, the brightness ratio between the reflectionand transmission modes can be changed without changing the area ratiobetween the reflective and transmissive electrodes by modifying the lensdesign, for example.

Alternatively, not all of those microlenses but only selected ones ofthem may have a bigger size than the picture element pitch P1 in the rowdirection. For example, by selectively increasing the sizes ofmicrolenses that are associated with the transmitting regions of pictureelements in one or two colors among the R, G and B picture elements, thebrightness of particular color(s) can be increased. Also, a viewabledisplay may be realized by changing the brightness on a color-by-colorbasis. Furthermore, if the R, G and B color filters have the samethickness, the decreased brightness of a particular color can becompensated for.

FIG. 7 is a plan view schematically illustrating an exemplary positionalrelationship among microlenses 57 a and 58 a, beam spot centers 41C andtheir associated transmitting regions Tr in a situation where only themicrolenses 57 a, associated with the transmitting regions of R, G or Bpicture elements, have an increased diameter. The beam spot centersformed by the microlenses shown in FIG. 7 are also arranged just likethose formed by the microlenses 54 a in FIG. 2.

In the examples illustrated in FIGS. 2, 3, 6 and 7, the microlenses arespherical lenses with a circular transmitting region. However, thepresent invention is in no way limited to those specific preferredembodiments. Alternatively, the microlenses may also be asphericallenses or Fresnel lenses. Also, the shape of the transmitting region maybe appropriately determined according to the beam spot shape, forexample.

The microlens preferably has a long focal length (i.e., the distancefrom the center of the microlens to the focal point). This is because ifthe focal length is long, the light beam emitted from the backlight unit50 can be collected on its associated transmitting region Tr just asintended even when the liquid crystal panel 100 includes a relativelythick substrate 10.

The microlens array 54 may be formed by a known method. Specifically,the microlens array 54 can be obtained by performing the followingprocess steps.

First, a die mold, reproducing the shape of the desired microlens array54 with precision, is prepared. Next, an UV curable resin is injectedinto the gap between the die mold and the substrate 10 of the liquidcrystal panel 100. Subsequently, the UV curable resin injected isexposed to, and cured by, an ultraviolet ray. After the UV curable resinhas been cured fully, the die is removed carefully.

According to this method, a microlens array with high optical propertiescan be manufactured easily with high mass-productivity. The material ofthe microlens array 54 is preferably a UV curable resin that exhibitshigh transparency and small birefringence when cured completely.Alternatively, the microlens array may also be formed by an ion exchangemethod or a photolithographic process.

In the preferred embodiments described above, microlenses are used asthe collecting elements. Optionally, prisms or any other type of opticalelements may also be used instead.

Hereinafter, the backlight unit 50 and display panel 100 for use in thetransflective LCD 200 of this preferred embodiment will be described.

Backlight Unit

The backlight unit 50 for use in this preferred embodiment is abacklight using a single LED as its light source. To get the lightcoming from the backlight unit 50 collected sufficiently by thecollecting element 54, the light emitted from the backlight unit 50preferably has a high degree of parallelism (e.g., the half width of thebrightness of the emitted light is preferably within ±5 degrees). Thebacklight unit 50 to be described below can emit light with a highdegree of parallelism in a predetermined direction.

As shown in FIG. 8, the backlight unit 50 includes a light guide plate24, a reflector 30 provided behind the light guide plate 24, an LED 21arranged close to a corner 24 t of the light guide plate 24 (see FIGS.10 and 12), and a prism sheet 25 provided in front of the light guideplate 24. The backlight unit 50 used in this preferred embodiment isdisclosed more fully by Kalil Kalantar et al. in IDW '02, pp. 509-512.

The light emitted from the LED 21 is incident on the light guide plate24 and reflected internally by the light guide plate 24. As a result,the light is transmitted through almost the entire outgoing plane of thelight guide plate 24. The light that has passed through the lowersurface of the light guide plate 24 is reflected by the reflector 30,incident on the light guide plate 24 again, and then transmitted throughthe outgoing plane of the light guide plate 24. The light that has goneout of the light guide plate 24 is incident on the prism sheet 25 andrefracted by the prism sheet 25 perpendicularly to the light guide plate24.

The reflector 30 may be made of an aluminum film, for example. The lightguide plate 24 may be made of some transparent material such aspolycarbonate or polymethyl methacrylate, for example. The light guideplate 24 includes a plurality of prisms 22 for getting the internallyincoming light reflected by reflective surfaces 22 a and thentransmitted through the light guide plate 24. Those prisms 22 are formedon the bottom of the light guide plate 24 and arranged in matrix asshown in FIG. 12. As shown in FIG. 8, each of the prisms 22 has atriangular groove shape with two reflective surfaces 22 a. Thereflective surfaces 22 a of the prisms 22 are provided so as to extendin an X direction (second direction) that is perpendicular to a Ydirection (first direction), which is the radial direction of a circledefined around the LED 21 as its center, as shown in FIG. 12. In otherwords, the prisms 22 are formed as grooves extending in the X direction.The tilt angle of the reflective surfaces 22 a is defined such that theinternal light in the light guide plate 24 can be efficientlytransmitted through the light guide plate 24 perpendicularly. In theexample illustrated in FIG. 12, the prisms 22 are arranged at regularintervals for the sake of simplicity. Actually, however, the prisms 22are preferably designed so as to have their intervals decreased as thelight travels farther away from the LED 21.

FIG. 9 shows the optical properties of the backlight unit 50 as measuredon the light outgoing plane thereof. The results shown in FIG. 9 wereobtained by averaging the brightnesses that were measured at threepoints A, B and C on three arcs drawn on the light outgoing plane of thebacklight unit 50 with the LED 21 defined as their center as shown inFIG. 10. In this case, the radial direction of a circle drawn around theLED 21 as its center is called a “Y direction” and the directionperpendicular to the Y direction is called an “X direction”.

As shown in FIG. 9, the brightness of the outgoing light in the Xdirection has a half width (i.e., FWHM) of about ±3 degrees, while thebrightness of the outgoing light in the Y direction has a half width ofabout ±15 degrees. Thus, it can be seen that the directivity is higherin the X direction than in the Y direction (i.e., the outgoing light inthe X direction has a higher degree of parallelism than that in the Ydirection). That is to say, definitely there is a difference indirectivity between the X and Y directions. Accordingly, the outgoinglight exhibits dispersed directivity on the light outgoing plane. FIG.11A schematically illustrates such a dispersion of directivity. FIG. 11Bshows what the ellipses shown in FIG. 11A mean. As can be seen from FIG.11B, the major-axis direction of the ellipse represents weak directivity(i.e., a low degree of parallelism), while the minor-axis direction ofthe ellipse represents strong directivity (i.e., a high degree ofparallelism).

In this manner, the outgoing light of the backlight unit 50 exhibitsdifferent directivities in the X and Y directions on the light outgoingplane. However, by using the microlens array 54, consisting ofmicrolenses 54 a having a circular cross section on a plane that isdefined parallel to the display screen (see FIGS. 1 and 2), even thehigh-directivity light in the X direction can be collected sufficiently.As a result, a high-brightness display is realized substantially overthe entire display screen of the LCD 200.

It should be noted that the backlight unit for use in this preferredembodiment does not have to have the configuration described above.Alternatively, the LED 21 may be arranged by the center of a sidesurface of the light guide plate 24 or even two or more LEDs may beused. Optionally, the LED may be replaced with a fluorescent lamp, forexample.

Display Panel

Hereinafter, the structure and functions of the display panel 100 foruse in the transflective LCD 200 shown in FIG. 1 will be described withreference to FIGS. 13 and 14. FIG. 13 is a plan view of the TFTsubstrate 100A of the display panel 100. FIG. 14 is a partialcross-sectional view of the display panel 100 including the TFTsubstrate 100A as viewed on the planes indicated by XIV-XIV in FIG. 13.

As shown in FIG. 14, the display panel 100 includes the TFT substrate100A, a color filter substrate 100B and a liquid crystal layer 23sandwiched between these two substrates 100A and 100B. A polarizer, aquarter wave plate and/or an alignment film (none of which is shown inFIG. 14) may be provided as needed for the TFT substrate 100A and colorfilter substrate 100B.

As shown in FIG. 13, the TFT substrate 100A included in the displaypanel 100 includes thin-film transistors (TFTs) 5, gate bus lines 1 andsource bus lines 2 on a transparent substrate of glass, quartz or anyother suitable material. As shown in FIGS. 13 and 14, a transparentelectrode 13 made of ITO, for example, and a reflective electrode 15made of Al, for example, are provided within each area surrounded withthe two gate bus lines 1 and two source bus lines 2, so as to make up apicture element electrode 4.

The TFT 5 is provided in the vicinity of each intersection between thegate and source bus lines 1 and 2. As shown in FIG. 13, the gate busline 1 is connected to the gate electrode 6 of the TFT 5 and the sourcebus line 2 is connected to the source electrode 7 of the TFT 5. Althoughnot shown in FIG. 13, if the picture element electrode 4 is arranged soas to overlap with the gate and source bus lines 1 and 2, the apertureratio of the picture element can be increased effectively.

As viewed from over the display panel 100 (i.e., perpendicularly to thedisplay screen thereof), each of the multiple picture elements Pxarranged in matrix includes a transmitting region Tr and a reflectiveregion Rf. The transmitting region Tr is defined by a region of the TFTsubstrate 100A that has the electrode function of applying a voltage tothe liquid crystal layer 23 and the function of transmitting theincoming light. On the other hand, the reflective region Rf is definedby a region of the TFT substrate 100A that has the electrode function ofapplying a voltage to the liquid crystal layer 23 and the function ofreflecting the incoming light.

On the transparent substrate 10 of the TFT substrate 10A, a gateinsulating film 12 is provided so as to cover the gate bus lines 1 (seeFIG. 13) and gate electrodes 6. A semiconductor layer 5 a is depositedon the gate insulating film 12 so as to be located right over the gateelectrodes 6. Also, the semiconductor layer 5 a is electricallyconnected to the source and drain electrodes 7 and 8 by way ofsemiconductor contact layers 7 a and 8 a, respectively, thereby makingup the TFT 5. The drain electrode 8 of the TFT 5 is electricallyconnected to the transparent electrode 13 and further connected to thereflective electrode 15 at a contact hole 9 of the resin layer 14. Thetransparent electrode 13 is provided on the gate insulating film 12 soas to be located around the center of the area surrounded with the gateand source bus lines 1 and 2.

The resin layer 14 with openings 14 a that expose the transparentelectrodes 13 is deposited thereon so as to cover almost the entiresurface of the transparent substrate 10. The reflective electrode 15 isprovided on the resin layer 14 so as to surround the openings 14 a. Thesurface of the resin layer 14 on which the reflective electrode 15 isprovided has unevenness like a continuous wave. Thus, the reflectiveelectrode 15 also has a similar surface shape and exhibits a moderatediffusion and reflection characteristic. The resin layer 14 with thecontinuous waveshape surface may be made of a photosensitive resin, forexample.

On the transparent substrate 11 (made of glass, quartz or any othersuitable material) of the color filter substrate 100B, a color filterlayer is provided and a counter electrode (transparent electrode) 18 isfurther provided thereon so as to face the liquid crystal layer 23. Thecolor filter layer includes red (R) color filters 16A, green (G) colorfilters, blue (B) color filters and a black matrix 16D filling the gapsbetween those color filters. In the LCD 200 of this preferredembodiment, the color filters are arranged in stripes as shown in FIG.16. The counter electrode 18 may be made of ITO, for example.

It should be noted that the display panel to be included in thetransflective LCD 200 does not have to have such a configuration but maybe any other known display panel. The display panel for use in thetransflective LCD 200 does not have to be a color display type but mayalso be a monochrome display type.

A display device according to any of various preferred embodiments ofthe present invention described above can increase the opticalefficiency without being limited by any particular picture elementarrangement and can be used effectively in a non-emissive display devicesuch as an LCD.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

This non-provisional application claims priority under 35 USC § 119(a)on Patent Application No. 2003-296179 filed in Japan on Aug. 20, 2003,the entire contents of which are hereby incorporated by reference.

1-9. (canceled)
 10. A display device comprising: a backlight unit foremitting light forward; a plurality of picture elements, which arearranged in columns and rows to define a picture element plane and eachof which has a transmitting region to transmit the light that has comefrom the backlight unit; and a plurality of collecting elements, whichare arranged in front of the backlight unit to transmit and collect thelight on the picture element plane, each of the collecting elementsbeing associated with the transmitting region of one of the pictureelements, wherein the light that has been transmitted through each saidcollecting element forms a beam spot on the picture element plane, thecenter of the beam spot being located within the transmitting regionassociated with the collecting element, wherein two beam spots, whichare the most closely adjacent beam spots formed on two of the pictureelements that are adjacent to each other in a row direction, have theircenters of mass shifted from each other in a column direction on thepicture element plane, and wherein the collecting elements and/or thetransmitting regions are arranged in a zig-zag pattern with apredetermined pitch across a substantial part of the display device in acertain direction.
 11. The display device of claim 10, wherein thecollecting elements and/or the transmitting regions are arranged in azig-zag pattern across a substantial part of the display device in a rowdirection.
 12. The display device of claim 10, wherein the pictureelements are arranged at a pitch P1 in the row direction and includefirst, second and third picture elements that are adjacent to each otherin the row direction, and wherein in the first, second and third pictureelements, the size of the collecting element associated with thetransmitting region of at least the first picture element is greaterthan P1 as measured in the row direction.
 13. The display device ofclaim 12, wherein the size of the collecting element associated with thetransmitting region of the second picture element and the size of thecollecting element associated with the transmitting region of the thirdpicture element are both greater than P1 as measured in the rowdirection.
 14. The display device of claim 10, further comprising acolor filter layer including red, green and blue color filters, whichare arranged in a striped pattern.
 15. The display device of claim 10,wherein the collecting elements make up an array of microlenses.
 16. Thedisplay device of claim 10, wherein each said picture element has aliquid crystal layer.
 17. The display device of claim 16, wherein eachsaid picture element has a reflecting region to reflect the light thathas come from the front of the display device, and wherein the displaydevice selectively conducts a display operation in each of atransmission mode and in a reflection mode.
 18. The display device ofclaim 17, wherein the transmitting region of each said picture elementis arranged such that the center of the transmitting regionsubstantially matches that of the beam spot.